The chick cardiovascular system will be used to substantiate the possible relationship between hemodynamic alteration and the formation of cardiovascular anomalies. Sympathomimetic amines--with and without adrenergic blocking agents--and methyl xanthines which have a synergistic effect on catecholamines will be administered to chick embryos at a stage of embryogenesis which has proven most sensitive to these compounds. Blood flow changes in the aortic arch system of each embryo will be captured on movie film which will be filed for subsequent data correlation. Such a procedure is valuable in that embryos are not subjected to any kind of trauma such as that induced by electrocardiogram microelectrodes or by microcatheterization employed in blood pressure experiments. This study, coupled with a parallel study to determine the role of catecholamines in abnormal cardiogenesis, can provide valuable clues to one or more mechanisms involved in congenital heart disease.